Electrical insulating tape and article formed therewith



July 25, 1961 w. H. MOEBIUS ET AL 2,993,949

ELECTRICAL INSULATING TAPE AND ARTICLE FORMED THEREWITH Filed 00 8, 1956 P -fil y: Iii j IN VEN TORt? W/LL/fiM H. Mose/05M; GEOBQE y. VEEEL/Wfi, 11. BY 4 9 "7' United States Patent 2,993,949 ELECTRICAL INSULATING TAPE AND ARTICLE FORMED THEREWITH William H. Moebius, Irvington, and George H. Vreeland, Jr., Butler, NJ., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Oct. 8, 1956, Ser. No. 614,387 6 Claims. (Cl. 174-124) Thisinvention relates to novel articles of manufacture and to methods for making them. In one of its more specific aspects the invention is directed to novel and improved flexible electric insulation capable of being employed as winding or wrapping elements around electrical components such as, cables, coils, etc.

For a good many years prior to the present invention, flexible insulation has been employed as winding or wrapping elements around electrical components and have been known to the art as varnished cambric, cable cloth, cable tape, etc. Such flexible insulation has been employed as helically wound coverings on electrical components to prevent dielectric breakdown from conductor to adjacent conductor or to ground, which condition is normally described as electric insulation. Said flexible electrical insulation commonly consists of a flexible base composed of a woven fabric such as cotton, glass, silk, etc. carrying a flexible impregnating and coating composition. The impregnating and coating compositions are generally of a resinous nature and are substantially infusible, and the surfaces thereof are sometimes tacky. Such coated bases employed as flexible electrical insulation heretofore have carried a film of mineral oil and/or mineral wax which in some instances are also a component of the resinous coating and impregnating composition. The mineral oil and/or mineral wax have been combined with such as resinous impregnating and coating compositions in either one of two ways. Generally 1-10 parts of mineral oil, for example, is mixed with 100 parts of the organic mass which is to be converted to the substantially infusihle state; then a flexible base is coated and impregnated with such mixture and subsequently heat cured to convert the organic mass to the resinous substantially infusible state. In the course of this curing step, the mineral oil bleeds or migrates outwardly to the surface of the coating to provide an oil film thereon. Still another method which has been followed in the prior art is to coat either one or both surfaces of the substantially infusible resinous impregnating and coating composition after curing with a film of mineral oil which is sometimes loaded with mica particles to increase its lubricity. In either case, whether the mineral oil is added before or after curing, the resultant flexible insulation material may be spirally wound in the form of a roll and is ready for storage and use. Or, after winding, the roll is transferred to the slitting operation, where the web of flexible insulation is unwound from said roll and slit into tapes of widths generally of A to 2 /2", which tapes are subsequently spirally wound in rolls and are ready for shipment and use.

The functions of the mineral oil and/or mineral wax employed on the substantially infusible resinous coating and impregnating compositions of such flexible insulation are as follows:

(1) To regulate or modify the surface of the resinous coating so that slitting is more readily accomplished.

(2) To facilitate unwinding from the wide roll when used in greater widths or in unwinding to the slitting machine and to facilitate unwinding of the rolled tape. In any of the aforesaid cases, to act as a physical barrier or separator to prevent the individual turns from adhering to each other while in rolled condition.

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(3) To provide the proper coeflicient of friction so that when the material is wound on an electrical component either by hand or machine, the proper amount of tension may be applied and the proper degree of slip is obtainable so that the tension applied to the material is so distributed as to permit the individual windings to conform to the configuration of the object being insulated.

(4) To prevent the helically wound individual turns from adhering to each other at the overlapping areas, i.e. they will not lock to each other although there will be some adhesion and the overlapping areas are capable of slipping on each other in the course of contraction, expansion or flexing of the element wrapped therewith.

The prior art flexible electrical insulations as well as components covered thereby have not always been entirely satisfactory from a slip or lubricity standpoint of such insulations where a mineral oil and/ or mineral wax has been employed as a film on the surfaces of the substantially infusible resinous coating and impregnating compositions. Their lack of uniformity has posed a manufacturing problem for a good many years, which we believe is due to the use of waxes and/or mineral oil. It is generally believed that the mineral oils which are used are only slightly compatible with the organic mass in the uncured state, and when mixed therewith and the mixture is cured after coating a base, the degree of compatibility of the mineral oil varies with the degree of cure. Consequently, the control of the amount of mineral oil on the surface is a very diflicult task. Also whatever method is used to provide the surface of the infusible coat with an oil film, the mineral oils, which are currently used for this purpose, vary considerably in viscosity and coefficient of friction with changes in temperature, so that the surface of the insulation has different characteristics under different temperature conditions. Where the mineral oil is applied to the substantially infusible resin coating after curing, it is difiicult to obtain uniformity because the amount of free mineral oil on the resinous coat may vary due to the solubility factor, however small, of the mineral oil with the particular run of infusible resinous coated base.

The present invention has been made to provide flexible insulating material whose lubricity or slip characteristic may be substantially duplicated time and time again in practically fool-proof factory production. And, by employing the present invention, it is possible to obtain lubricity as high as that obtained by using mineral oil and mica, but without the use of either.

Illustrative embodiments of the present invention are shown in the drawings, wherein:

FIG. 1 is a perspective view of a roll of tape embodying the present invention.

FIG. 2 is an enlarged cross sectional view of the tape shown in FIG. 1 and is taken on line I-I-II of FIG. 1.

FIG. 3 is a view in side elevation of a conductor having a tape shown in FIGS. 1 and 2 helically wound therearound, with the adjacent windings thereof being in partially overlapping relationship.

FIG. 4 is an enlarged fragmentary cross sectional view taken on line IVIV of FIG. 3.

According to this invention, a flexible base 10 is employed which in general, is a flexible, fibrous material composed of paper, cotton, glass, silk, Orlon, nylon, Dacron, etc. fibers or filaments yarns or threads which may be woven or non-woven, and if the latter in the form of a matted or felt-like base. In general, the thickness of said base 10 is in the range of about 1-6 mils. Said base 10 is impregnated and coated with a thermosetting organic mass in a solvent. Then the impregnated and coated base is first heated to drive off the solvent and then heated to higher temperature to convert the thermosetting organic mass to the substantially infusible state whereby said base 10 is coupled with a substantially solid and infusible impregnant and coating 11. The resultant material (I) may be 36 to 52" in width and measures in thickness in the range of about 5-15 mils, depending upon the thickness of base employed and is of any length desired depending upon the length of the base 10* so treated. The surfaces of said resultant material (I) may be of a tacky nature and if so when the material is wound in rolls, there is a great tendency of the faces of adjacent windings to adhere to each other. Said resultant material (I) has good insulation characteristics in that its dielectric strength is at least 1000 volts per mil at 70 F. as measured by the IPCEA method and dissipation factor at 185'F. is no greater than .08, and has good flexibility characteristics in that it is capable of being helically wound around a mandrel about A in diameter without cracking.

Such resultant materials (I) in general, may be produced in the manner known to the art, with some of them having been on the market for a good many years prior to this invention. The thermosetting organic mass employed in the production of such resultant materials may consist of (a) one or a combination of two or more heat polymerizable unsaturated fatty oils of vegetable, animal or marine origin, examples of which are linseed, castor, soya-bean, China wood, oiticica, perilla, safflower, fish oils and the like as well as such fractions thereof which are heat polymerizable to the substantially infusible state it being understood that said oils and/or fractions may be in the raw, refined, blown and/ or heat bodied state; or (b) natural or synthetic resinous material capable of being heat converted to the substantially solid state, examples of which are one or more resinous materials, such as phenol-aldehyde, furfuralketone, terpene, alkyd, phenolic ether resins, polyester resins, etc. or (a) and (b) may be combined with each other and in such cases oil-soluble resins are combined with (a) in any desired proportion but generally 13 parts by weight of (a) are used with 9-1 parts of (b) and such mixtures are heated to solution before application; or such mixture of (a) and (b) may be mixed with one or a combination of two or more bituminous materials, gilsonites, vegetable, animal and marine pitches and pitchy residues which are also oil soluble and such mixtures are heated to the desired viscosity. In any case, there is added a diluent or thinner and one or a combination of the well-known metallic driers, examples of which are the manganese, copper, lead, cobalt, iron, zinc, platinum, nickel, rhodium salts of various organic acids, such as naphthenic, abietic, oleic, resinic acids, etc. and of other organic substance, such as tall oil, etc.

It is, of course, to be distinctly understood that such resinous masses which serve as coatings 11 for the bases 10 employed in the practice of the present inoculation, may, if desired, be composed of other substantially infusible resinous masses than those specifically enumerated herein and may include as components thereof various pigmenting agents. However in all cases, the materials (I) employed in the practice of this invention are characterized by the base 10 carrying a substantially infusible resinous coating 11 and having the electrical and physical characteristics heretofore set forth.

The following are specific examples of such materials (I) and methods for producing them. These examples are given much by way of illustration and not limitation, all parts being given by weight, unless otherwise specified.

Example IA 100 pounds of dehydrated castor oil (Castung G-H), 75 pounds of an oil soluble phenol-aldehyde resin (Bakelite 254) and 113 pounds of blown petroleum pitch (Robertson 292) were heated together for 30 minutes at 580- 600 F. until the mass acquired a 2 cm. flow charactersequently, 292 pounds of mineral spirits and 2 pounds of naphthenate metallic driers, containing 15.5 grams of manganese and 83.4 grams of lead, were added and agitated to provide a homogeneous mass. This mass was then filtered and using an edgewise coa-ter, was applied to a cotton cloth (4.5 mils, count 6460) to impregnate and coat the same. Three coats were applied with each maintained for 20 minutes at approximately 325 F. resulting in a cable cloth whose overall thickness measured 12.3 mils average and whose coating was substantially infusible.

A sample of this finished material hereinafter known as material IA was subjected to various tests and the following characteristics were ascertained:

Dielectric strength (IPCEA) was 1160 volts per mil at 70 F.; dissipation factor at F. is .0365, surface characteristic was sticky and tacky.

Example HA The entire quantity of material IA was cut in half and one half was subjected to hydrogenation in the manner set forth in the patent to M. T. Harvey, 2,554,826, of May 29, 1951. After hydrogenation, a sample of this material hereinafter known as material IIA was subjected to the same tests as material IA and the following characteristics were ascertained:

Dielectric strength (IPCEA) was 1200 volts per mil at 70 F.; dissipation factor at 185 F. was .0361; surface character non-tacky and rubbery.

Example IIIA 384 pounds of KVO linseed oil was placed in a copper kettle and heated to and maintained at a temperature of 580600 F. until it had attained a body of Z-S. Then there was added thereto 77 pounds of Z-5 bodied linseed oil and the mixture was heated to 300 F. This combination was mixed to uniformity and then it was thinned by adding thereto 292 pounds of mineral spirits. This coating composition was then applied to a 4.5 mil 64 x 60 thread count cotton sheet to impregnate and coat the same. Two coats were applied with each individually maintained for 30 minutes at approximately 300 F. resulting in a cable cloth whose over all thickness measured 6 mils average and whose coating was a substantially therrno-set and substantially infusible resin. This material is hereinafter known as material IIIA and was tested and the following characteristics were ascertained:

Dielectric strength (IPCEA) was 1000 volts per mil at 70 F.; dissipation factor at 185 F. was 0.04; surface character was substantially non-tacky.

According to this invention, either one or both faces of such materials (I), examples of which are materials IA-IIIA, has a layer or coating 12 of a silicone fluid thereon. Such layer or coating 12 is present thereon as a substantially uniform continuous layer or coating over substantially the entire surface of the face coated. The thickness of the layer or coating 12 of silicone fluid is such as to provide a substantially continuous layer or coating over the entire surface of the face coated, and in general is at least 001 gram per square yard of surface of the individual face of said material coated therewith, and for most purposes the maximum amount of silicone fluid employed is about 6 grams per square yard surface of the individual face of said material coated therewith.

Such silicone fluids employed in the practice of this invention have the following characteristics: they are substantially incapable of forming solutions with said substantially infusible resinous components of said materials (I); they are normally liquid and are liquid at temperatures in the range of 30 F. to 300 F.; they have a viscosity at 77 F. in the range of 20 to 2000 centistokes; they have a viscosity at 185 F. in the range of 7-1000 centistokes. Such silicone fluids are commercially available as mixtures of different molecular weight polysiloxanes of an homologous series. The commercially available silicone fluids may be used as such or two or gallons of the latter. layer of solution, the so coated material IA is passed 5 more of them may be blended together to obtain other silicone fluids useful in the practice of this invention.

The silicone fluids which are preferably employed in the practice of this invention are the fluid alkyl polysiloxanes having a viscosity at 77 F. in the range of 30 to 1000 centistokes, and at 185 F. in the range of 12 to 400 centistokes.

Such silicone fluids which are preferably used in the practice of ,this invention are dimethyl polysiloxanes which are available commercially as Dow Corning DCv-200 Fluids, Union Carbide and Carbon Silicone Fluids L45, General Electric Company SF-96 Silicone Fluid, either individually or blended to obtain silicone fluids of the desired viscosity.

In general, the novel materials 9 of this invention may be produced by coating one or both sides of materials (I), examples of which are materials IA-IIIA, with a solution of one or a combination of two or more of such silicone fluids, after which the solvent of said solution is driven off leaving behind on the resinous coating 11 of said material (I) employed a layer or coating 12 of the silicone fluid employed, with said layer or coating 12 being substantially continuous over substantially the entire surface thereof. Because of the particular nature of the silicone fluid employed, it will not migrate into nor appreciably form solution with the resinous surface of material (I) but will remain thereon as a coating 12. After the evaporation of the solvent, the material (I) now coated-With a layer 12 of such silicone fluid will be substantially dry to the touch even in those cases where the original surface of material (I), such as material IA for example, was normally tacky to the touch. Then the silicone fluid coated material (I) may be wound in the form of a roll or, if desired, may first be slit to provide tapes 9 of the desired widths and may be subsequently wound to provide a roll of tape as shown in FIG. 1 and in many cases is ready for storage, shipment, and use.

Other methods may be employed for applying such silicone fluids, such as, by molecular distillation of the fluid in vacuo and deposition of fluid in gaseous state or spraying of fluid and in either case with or without subsequent wiping or wiping the fluid on surface of material (I).

The novel materials of this invention and methods for making same, all given by way of illustration and not limitation, all parts given by weight unless otherwise specified.

Example 1 A sheet of material IA measuring about 40 inches wide and 500 feet long is continuously coated on one of its faces across the entire width thereof with a solution layer of substantially uniform thickness. Said solution consisting of a Union Carbide and Carbon Silicone Fluid L45 (viscosity at 77 F. of 350 centistokes) dissolved in VM&P naphtha, with the ratio of the Silicone Fluid L45 to the naphtha being 288 grams of the former to After the application of said through an oven at 300 F. to drive off the VM&P naphthasolvent from said solution layer, thereby leaving 'behind on said coated surface silicone fluid in the form of an extremely thin continuous film covering substan tially all of one of the resinous faces of said material IA, and measuring about .5 gram per sq. yd. of said surface coated.

Example 2 Employ the same procedure as that set forth in Example 1, except that material IIA measuring 40" in width and 500 feet in length is coated on one side with a solution consisting of a blend of Dow Corning DC-200 Fluids dissolved in a VM&P solvent. The blend consists of 2 Dow Corning DC200 Fluids respectively having following are specific examples of some of the viscosities at 77 F. of 1000 and 350 centistokes, with the viscosity of the blend being 650 centistokes at 77 F. The solution applied to the surface of material IIA consists of such blend dissolved in VM&P naphtha, solvent with the ratio of the blend to solvent being 576 grams of the former to 5 gallons of the latter. The resultant material is material IIA having one face thereof completely coated with a substantially continuous layer of such blend measuring about 1 gram of such blend per square yard of that face.

Example 3 Employ the same procedure as that set forth in Example 1 except that material IHA measuring 40" in width and 500 feet in length is coated on both sides with a solution consisting of a Dow Corning DC-ZOO Fluid having a viscosity at 77 F. of 50 centistokes and dissolved in VM&P naphtha solvent. Said solution consists of the Dow Corning DC-200 fluid and the solvent in the ratio of 864 parts of the former to 5 gallons of the latter. The resultant material is material IIIA having each of both sides thereof completely coated with a substantially continuous layer of Dow Corning DC-200 Fluid measuring about 1.5 grams of such DC-200 Fluid per square yard of surface covered.

Such silicone fluid coated materials, examples of which are shown in Examples 1-3 of this invention, because the surface of materials (I) has been so modified, are more easily and readily slitted. In addition, the presence of said silicone fluid as a coating 12 on such materials (I) facilitatm unwinding from the wide roll when used in greater widths and also in unwinding to the slitting machine, and inaddition, facilitates unwinding of the rolled tapes, an example of such roll of tape being shown in FIG. 1. In any of the aforementioned cases it acts as a physical barrier or separator to prevent the individual turns from adhering to each other while in rolled condition, as shown in FIG. 1, over the wide temperature range normally encountered in storage, shipment, and use. Moreover, the presence of the silicone fluid layer 12 pro vides a surface having the proper coefficient of friction so that when the material, either in greater widths or in tape widths, is wound on an electrical component, either by hand or machine, the proper amount of tension may be applied and the proper degree of slip is obtainable so each other in the course of contraction, expansion, or flexing of the element insulated therewith. Also, the presence of the silicone fluid layer 12 does not in any manner adversely affect the insulation characteristics or the flexibility of the material (I) to which it has been applied.

On the contrary, the flexibility of the cloth or tapes embodying this invention is such that they may be helically wound around a mandrel /8 in diameter without cracking and the insulation characteristics thereof are enhanced so that in all cases their dielectric strengths are at least 1000 volts per mil at 70 F. as measured by the IPCEA method and their dissipation factors at F. are always no greater than .08.

Such novel materials of this invention, examples of which are found in said Examples 1-3 may be wound in roll form and such rolls may be stored, shipped and are ready for use, or after winding in roll form, the roll may be unwound and slitted to provide tapes of any desired width and generally /1 to 2 /2". Such tapes are spirally wound in roll tapes, an example of which is shown in FIG. 1, measuring any desired length and generally 200 feet or more and are ready for storage, shipment and use.

Such rolls of the wider novel materials of this invention as well as the rolled tapes find especial utility as insulators for electrical components. Generally for this purpose they are helically wound around an electrical component which may be an electric cable or the like to insulate such electrical component.

When an electrical component, which of course is an electrical conductor, such as a wire 20 or cable, etc., is to be insulated with such materials (I) having only a single face thereof coated with such silicone fluid, as illustrated in Examples 1 and 2, obviously care must be taken to properly face such silicone coated materials (I) for winding on such components. Obviously the layer 12 of silicone fluid thereof should be disposed on the electrical component if a bare component 20 is to be insulated therewith and, such novel materials of this invention are helically wound around said component 20 to provide helical "windings in overlapping relationship, with the silicone fluid layer 12 of each individual winding located between the conductor 20 and the base 10 of such winding, as shown in FIGS. 3 and 4.

It is to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described and all statements of the scope of the invention which as a matter of language might be said to fall therebetween, and that they are intended to be inclusive in scope and not exclusive in that, if desired, other materials may be added to our novel materials herein claimed Without departing from the spirit of the invention. Particularly it is to be understood that in said claims ingredients or components recited in the singular are intended to include compatible mixtures of said ingredients wherever the sense permits.

We claim:

1. A roll of electrical, insulating tape, said tape comprising a flexible base carrying a substantially infusible resinous coating, said resinous coated base having a dielectric strength of at least 1000 volts per mil at 70 F. measured by the IPCEA method, a dissipation factor at 185 F. no greater than .08 and a flexibility characteristic such that it is capable of being helically wound around a mandrel without cracking, a layer of silicone fluid carried by said coated base, said silicone fluid being liquid at temperatures in the range of 30 to 300 F., having a viscosity at 77 F. in the range of 20-2000 centistokes, and having a viscosity at 185 F. in the range of 7-1000 centistokes, said tape measuring about -15 .mils in thickness.

2. An electric conductor in combination with a tape defined in claim 1, with said tape being in the form of helical windings, with adjacent windings being in overlapping relationship, and with said layer of silicone fluid on each individual winding located between said base of said winding and said conductor and between bases of adjacent windings in overlapping relationship.

3. A roll of electrical, insulating tape, said tape comprising a flexible base carrying a substantially infusible resinous coating, said resinous coated base having a dielectric strength of at least 1000 volts per mil at 70 F. measured by the IPCEA method, a dissipation factor at 185 F. no greater than .08 and a flexibility characteristic such that it is capable of being helically wound around a Mr" mandrel without cracking, a layer of silicone fluid carried by said coated base, said silicone fluid being liquid at temperatures in the range of 30 to 300 F., having a viscosity at 77 F. in the range of 20-2000 centistokes, and having a viscosity at 185 F. in the range of 71000 centistokes, said silicone fluid being alkyl polysiloxane, said tape measuring about 515 mils in thickness.

4. A roll of electrical, insulating tape, said tape comprising a flexible base carrying a substantially infusible resinous coating, said resinous coated base having a dieelectric strength of at least 1000 volts per mil at F. measured by the IPCEA method, a dissipation factor at F. no greater than .08 and a flexibility characteristic such that it is capable of being helically wound around a Va" mandrel without cracking, a layer of silicone fluid carried by said coated base, said silicone fluid being liquid at temperatures in the range of 30 to 300 F., having a viscosity at 77 F. in the range of 20-2000 centistokes, and having a viscosity at 185 F. in the range of 7-1000 centistokes, said silicone fluid being dimethyl polysiloxane, said tape measuring about 5-15 mils in thickness.

5. A roll of electrical, insulating tape, said tape comprising a flexible base carrying a substantially infusible resinous coating, said resinous coated base having a dielectric strength of at least 1000 volts per mil at 70 F. measured by the IPCEA method, a dissipation factor no greater than .08 and a flexibility characteristic such that it is capable of being helically wound around a mandrel without cracking, said resinous coated base carrying an outermost layer of a silicone fluid measuring in the range of about .03 to 6 grams per square yard of the surface of said resinous coated base, said silicone fluid being liquid at temperatures between 30 F.-300 F., having a viscosity at 77 F. in the range of 30-1000 centistokes and a viscosity at 185 F. in the range of 12-400 centistokes, said tape measuring about 5-15 mils in thickness.

6. A roll of tape, with individual turns of said roll comprising a flexible base being about 1-6 mils in thickness and carrying a substantially infusible resinous coating, said resinous coated base being about 515 mils in thickness and having a dielectric strength of at least 1000 volts per mil at 70 F. measured by the IPCEA method, a dissipation factor at 185 F. no greater than .08 and a flexibility characteristic such that it is capable of being wound around a /s" mandrel Without cracking, a layer of silicone fluid on said resinous coating, said silicone fluid being liquid at temperatures in the range of 30 F.-300 F., having a viscosity at 77 F. in the range of 20-2000 centistokes and having a viscosity at 300 F. in the range of 7-1000 centistokes.

References Cited in the file of this patent UNITED STATES PATENTS 2,133,183 Baird et al. Oct. 11, 1938 2,492,568 Gillis Dec. 27, 1947 2,516,030 Swiss July 18, 1950 2,624,777 Abbott et al. Jan. 6, 1953 2,626,223 Sattler et a1. Jan. 20, 1953 2,654,681 lJueck Oct. 6, 1953 2,768,906 James Oct. 30, 1956 FOREIGN PATENTS 609,366 Great Britain Sept. 29, 1948 695,703 Great Britain Aug. 19, 1953 OTHER REFERENCES Dow Corning Silicone Notebook, Fluid Series No. 3 (30 pages, 8 relied upon), September l948. 

